Wasp Larva Disinfects Roach From Within

For a roach lover, this wasp (right) is a hygiene freak: its larva disinfects the innards of the host while it devours it from within. Gudrun Herzner

Cockroaches feed on garbage and carrion, so anything that’s devouring a cockroach from the inside out must contend with a variety of disease-causing microbes. Now, German scientists have shown that the larva of the emerald cockroach wasp actively disinfects its roach host by exuding antibacterial chemicals from its mouthparts.

The scientists published their findings in the journal Proceedings of the National Academy of Sciences¹. Emerald cockroach wasps (Ampulex compressa) begin their life on an American cockroach (Periplaneta americana) which the mother wasp stings. Once it’s been dragged back to a burrow, she sticks one of her eggs into it. When it hatches, the wasp larva burrows through the immobilized roach and feasts on its innards, eventually killing it.

Gurdrun Herzner, from the University of Regensburg in Germany, watched the larvae by installing transparent panels into the sides of parasitized roaches, providing a direct view of what was going on in its innards. The larvae regularly slathered large amounts of clear liquid onto their hosts’ tissues.

The team analyzed the liquid and discovered that it contained mellein and micromolide, two substances that slow the growth of certain microbes, like Serratia marcescens. If left unchecked, S. marcescens can rapidly kill insect larvae.

There are more than 80,000 species of parasitoid wasps. Another species, Pimpla turionellae secretes antibacterial chemicals from its anus while it’s inside its moth host. The European beewolf (Philanthus triangulum) preserves honeybees for its larvae by embalming them in oily secretions, which stops water from condensing and fungi from growing.